Cyclopropenoid fatty acids (CPFA) which occur in certain foodstuffs such as cottonseed oil and flour, kapok oil and okra are known to have toxic effects when consumed by animals. These unique compounds are known to impair reproduction in rats and chickens, alter the fatty acid composition in the body lipids of several species, and cause characteristic alterations in trout and rabbit liver parenchymal cells. In addition, our studies have demonstrated that CPFA act as powerful cocarcinogens with aflatoxin B1 and as carcinogens in the induction of liver cancer in rainbow trout. Cyclopropenes are postulated to bind with proteins and enzymes through a nonreversible reaction with free sulfhydryls. The current mechanistic study of the cyclopropene-sulfhydryl reaction will confirm or refute this theory. The cyclopropene-sulfhydryl reaction is not spontaneous as previously suggested in the literature. This research will determine the biological conditions and the mechanism by which this reaction does take place and the degree of competition from other olefins. The NMR spectra of cyclopropenes in bio-materials is being studied.